1. A female who accompanies her male friend(s) out and then prevents them from getting any attention from other females by her mere presence. Other females will think she is his girlfriend. So then if he tries to run his game, he looks like the asshole who is hitting on other girls right in front of his "girlfriend."

2. An ugly girl who comes out with her cute girlfriend(s) and prevents the cute girls from getting any game.

3. "Girls' night out." This is a cockblocker by virtue of its name and implications. There will inevitably be a girl or two in this group who are man-haters. They will brainwash their cute girlfriends into thinking men are bad, players, jerks. They will convince their cute girlfriends that girls need to stick together, no men tonight.

1. Joe: Does Judy really need to tag along with us tonight? She's such a cockblocker, everyone thinks she's my girlfriend!

2. Cody: Hey Trevor, that girl is cute. Will you be my wingman and distract her ugly friend while I go talk to her? Trevor: No way dude, her friend is hideous!

In this situation, the ugly girlfriend is cockblocking her cute girlfriend.

Cockblocker: 1. (noun) a female friend who accompanies another female friend to planned meetings with a male peer, to ensure that the sista does not get into trouble;
2. (Noun) a male who interferes with another male's attempt to freak the woman whom the former either wishes to protect as a friend, or is already pursuing himself;
3. (Verb) to cockblock: basically, to interfere, by way of one's mere presence, with the attempt of one person to freak another

1. Jill "Jane, I really need you to come along tonight as my cockblocker so I don't do anything I would later regret.
Jane "Sure"
2. I made my move toward that hottie Jennifer with the thought of grinding with her. That cockblocker Alex cut in and got it first.
3. Alex cockblocks all the time

An insecure asshole who does not have the balls to open a conversation with a woman, but will not hesitate to butt into any interaction already in progress. They will then proceed in destroying any chance of a hook-up. Most times, what they refer to as "their game" is so poor that not only do they fuck up YOUR prospects they end up scaring away the "prey" to another table or "Lance Goodthrust" at the other end of the bar. They are the most effective birth control device known to mankind. Stay away from these people or become a monk where you'll have just as much opportunity for getting some pussy.

You're talking to a hottie that you've managed to cut away from her heard. You're just about to "close the deal" with a number or invite to a more secluded place ie. your car, when "CB" shows up and hangs over you both like a plague from God or bad breath or herpes. The conversation, which had been flowing with magical bullshit, becomes strained and uncomfortable. She mentions that "it's getting late" as she eyes the safety of the heard. Her departure is followed by, "She was a bitch anyway!" from the asshole who's just ruined it for you. You supress the urge to punch him in the liver, move to another part of the bar where you start again in the hopes that he cannot find you. For surely he is the Devil.